In a hospital setting it is desired to monitor a number of different patients at the same time by means of one monitoring system that acquires data related to the vital signs, i.e. the physiological status of the patients and provides the nursing staff with respective notifications about their status. For a setting with non-critical patients who are able to move freely within the hospital, wireless systems have been developed that comprise monitoring units that can be worn by the patients. These monitoring units comprise sensors for monitoring the vital signs and means for transmitting corresponding physiological data to a host system. To cover the area completely in which the patients are located, different access points (so-called hotspots) are arranged so that a patient wearing a monitoring unit is always in reach of one of these access points to provide a wireless communication with the host system.
In an ideal situation each monitoring unit of the patient monitoring system is always in reach of an access point so that a communication between the monitoring units and the host system is established at any desired point of time. However, in practice such a complete monitoring cannot be guaranteed. It may happen that the patient wearing a monitoring unit enters a zone that is not covered by the reception area of any access point, so that the communication between the monitoring unit and the host system is interrupted. This is the reason why the time of the measurement of physiological status data and the time of transmission of these data are decoupled. When the host system determines that no data transmission has occurred according to the predetermined time schedule, an alarm is activated to notify the nursing staff that no physiological data related to the respective patient are present in the system and that no monitoring of this patient takes place. However, this may result in situations in which the nursing staff is alarmed only because of an interruption of the connection although there is no critical status of the patient to be cared for.
US 2004/0236189 A1 discloses a patient monitoring system comprising a wireless network with monitoring units that communicate with a modem as a central monitoring station. When the monitoring units fail to communicate on time schedule, the modem generates an alert. However, the generation of this alert is based on a fixed time schedule, leading to the same problems as described above, namely to the generation of many faults alarms due to a non-critical temporary interruption of the connection between the monitoring unit and the network.